Torque limiting wrench

ABSTRACT

A power tool having an adjustable torque-limiting coupling and a shut-off means, the coupling (or clutch) consisting of a driving member, a co-axial driven member and a coupling assembly comprising a tapered helical spring and means for adjusting the position of the spring on the driving and driven members, and the shut-off means sensing relative movement between the driving and driven members, and effecting shut-off.

BACKGROUND OF THE INVENTION

This invention is a novel torque-limiting apparatus particularlyadaptable to power wrenches. It is a torque-responsive coupling operablein response to a selected torque load to break the driving connectionbetween an input (driving) member and an output (driven) member. Thisinvention further incorporates shut-off means for de-energizing thepower supply in response to a pre-determined torque load.

Previously, clutch mechanisms incorporated with shut-off controlsundesirably transmitted inertia forces, and were unduly sensitive to the"hardness" of a joint. Also, the prior mechanisms were found to besensitive to many variables in addition to the joint hardness, such asair pressure in pneumatic tools, differences in lubrication of thefasteners and of the tools, and motor inertia. For example, referencemay be made to U.S. Pat. Nos. 3,370,680, 3,515,251, or 3,195,704, eachof which is believed to disclose mechanisms characterized by one or moreof the aforementioned problems. In addition, torque-limiting devicesfrom other areas of the art, such as U.S. Pat. Nos. 3,782,515 and1,126,780 are believed to lack certain desirable features provided bythe instant invention.

It is a principal object of this invention to provide an improvedadjustable torque-limiting coupling that is relatively insensitive tovariations in many variables that normally affect output torque.

It is a further object to provide an improved torque-limiting couplingthat is easily adjustable for a pre-set torque and offers greaterrepeatable accuracy.

It is a further object of this invention to provide a novel adjustabletorque-limiting coupling that can be used with a variety of shut-offdevices to interrupt the flow of power to the power source.

Another object of this invention is the provision of an adjustabletorque-limiting apparatus that is relatively straight-forward inconstruction, easy to maintain and repair, and dependable in operation.

SUMMARY OF THE INVENTION

This invention pertains to an adjustable torque-limiting unit which, ina presently preferred embodiment, couples a driving shaft to a drivenshaft by means of a spring of variable cross-section, so that therelease force is a direct function of the cross-sectional area of thespring overlying the interface between driving and driven members.Adjustment is accomplished by moving the spring axially so that thecross-sectional area of the spring is varied at this place. Thethickness of the coil (and thus the cross-sectional area) determines thetorque transmitted to the output member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view, partly in section, of a pneumatic power wrenchcontaining the torque-limiting unit coupled to one type of shut-off;

FIG. 2 is a view of the front end of a wrench partly in section, with analternate type of shut-off; and

FIG. 3 is a section through FIG. 2 on the line 3--3.

DESCRIPTION OF THE INVENTION

The adjustable torque-limiting coupling of this invention is shown hereas it is incorporated in a pneumatic nut runner. It will readily beperceived, as the description progresses, that this clutch, or coupling,can also be used in electric nut runners, and in many otherapplications. Also in FIG. 1, the clutch is shown as installed betweenthe pneumatic motor and the reduction gearing, while in FIG. 2 thecoupling is installed after the gear train. This unit could even be madeas an attachment for existing nut runners -- as an external, "add-on,"accessory. However, when built-in as shown here, the coupling can beincorporated with an automatic shut-off to cut the power supply (in thiscase, air) to limit wear on the clutch (coupling).

FIG. 1 shows a pneumatic nut runner 10, of the "pistol" type, having aconventional fluid motor 12 mounted therein as the driving means. Fluidis furnished via a hose (not shown) connected to an inlet 14 at thebottom of the handle 16. Passages (indicated schematically on FIG. 1)and a control valve (not shown) operated by trigger 18 admit fluid tochamber 20 at the rear of the tool. From this chamber 20, fluid flowsthrough opening 22 and passages 24 to motor 12. All the above isconventional and well-known in the art. The motor shaft is supportedupon bearings 23 and 25, and is of conventional construction, with theinput drive spindle 26 splined to the motor shaft. Spindle 26 isexternally threaded at 28 with left-hand threads to accept torqueadjusting nut 30 and lock nut 32. Torque adjusting nut 30 has anelongated body 34 with a threaded portion 36 at one end and a spacer 38and retaining ring 40 seated in the other end, and encloses coil spring42. Spring 42 (right-hand wound) fits tightly on input drive spindle 26and also fits tightly around output drive spindle 44. This coil springhas a constant inside diameter in the relaxed condition and thisdiameter is very slightly smaller than the outer diameter of input drivespindle 26 and output drive spindle 44. Spring 42 has the outer diameterof its coils machined in a taper, with the small end on the outputspindle. Torque adjusting nut 30 is threaded on input spingle 26 and, byadjusting the position of nut 30 on spindle 26, positions spring 42axially along the input spindle. This determines the particular coil ofspring 42 that links input spindle 26 to output spindle 44, which inturn apparently determines the amount of torque transmitted. Any forceabove the amount of torque selected merely causes the coils on outputspindle 44 to slip over the outer surface of spindle 44. Torqueadjusting nut 30 is retained in the desired position by lock nut 32. Inthe embodiments shown here, the torque adjustment is accessible byunscrewing the forward position 46 of the tool from the body of thetool, then reaching into the torque adjusting nut 30 and the lock nut 32with a tool properly adapted to fit the nuts, such as a spanner.

In the embodiment shown in FIG. 1, the rotating motion is transmittedfrom output spindle 44 to planetary gearing 48 which is only partiallyshown here as it is too well-known in the art to need description. Fromthe gearing 48, the torque is transmitted to nosepiece 50, which can beany suitable tool holder for the purpose.

In the embodiment shown in FIG. 2, the clutch or coupling is placedafter the gearing, adjacent the nosepiece 50, which is shown as anintegral part of output spindle 44.

The clutch described above is the presently preferred embodiment. Itwill be obvious to those skilled in the art, however, that the couplingadmits of a number of alternate configurations, such as reversing thespring 42 to place the small end on the input drive spindle 26, orplacing spring 42 inside input drive spindle 26 and output drive spindle44, bearing against the inside of these hollow drive spindles.

In order to minimize wear on the clutch parts, it has been combined witha shut-off mechanism in these figures. Both shut-off mechanisms senserelative rotation between the input drive spindle 26 and the outputdrive spindle 44 and move a valve 52 in chamber 20 to close opening 22.In both embodiments, valve 52 (only shown in FIG. 1) is held closed bythe incoming fluid pressure until the operator releases trigger 18, atwhich time the inlet fluid flow 54 is interrupted and chamber 20 isvented to atmosphere through vent 56, all in a manner well-known in theart.

In the embodiment of FIG. 1, an end face 58 of input drive spindle 26has fixed to it (or integral therewith) an annulus of cam teeth 60arranged concentrically about the longitudinal axis of the tool.Attached to open-ended cylinder 62, and meshing with teeth 60, is a likecam with teeth 64. Cylinder 62 is slidable in output spindle 44, but islinked by pin 66 to spindle 44 to rotate therewith. Pin 66 islongitudinally slidable in slot 68. Slot 68 is as wide as the distanceof one tooth to another of cam 64, which permits pin 66, cylinder 62 andteeth of cam 64 to always engage, regardless of the position that outputspindle 44 stops with respect to input spindle 26. The assembly ofcylinder 62, pin 66 and cam 64 is biased by spring 70 toward engagementwith cam 60, which is longitudinally fixed. Attached to the closed endof cylinder 62 and running through the hollow shaft of fluid motor 12 isa push rod 72 which engages stem 74 of valve 52. During normaloperation, teeth 60 and 64 are engaged under the bias of spring 70. Whenthe set torque is reached, input spindle 26 moves rotatably relative tooutput spindle 44, and teeth 64 ride up on teeth 60 against the bias ofspring 70. This moves cylinder 62 and push rod 72 to the right as seenin FIG. 1, allowing valve 52 to close under the impetus of the pressuredifferential. This pressure differential keeps valve 52 closed until theoperator releases trigger 18, which vents chamber 20 to atmospherethrough passage 56. When the pressure on valve 52 is thus equalized,spring 70 acts to push cylinder 62 and push rod 72 back to the left asseen in FIG. 1. Teeth 60 and 64 of the cams go back into mesh, restoringvalve 52 to the position shown in FIG. 1, and readying the tool for useagain.

In the embodiment of FIGS. 2 and 3, the operation of the tool and clutchare the same, and like parts have been given like numbers. The porting,shut-off valve, and fluid motor are the same and are not shown in FIG.2. The means of retaining push rod 72 differs in this embodiment fromthat shown in FIG. 1, and resembles U.S. Pat. No. 3,195,704 in somerespects. In this embodiment, axial movement is confined to push rod 72and valve 52. A release member 76 is pivotally mounted on the drivenmember 44 by means of a suitable pin 78. This release member 76 isnormally urged to a cocked, or set, position by a small transversespring 80. The release member is notched as at 82 to allow movement ofthe push rod, but in its cocked position the release member is held suchthat the notch is not aligned with the rod, and an end of the releasemember will engage the end of the rod, as shown in FIG. 2. When the toolis not being operated, push rod 72 is biased to the left as seen in FIG.2 by spring 84. This moves push rod 72 to the left, allowing releasemember 76 to assume the position shown in FIG. 2 under the influence ofspring 80.

During the operation of the tool, the above-described position of therelease member 76 and push rod 72 keeps the valve 52 open, allowing themotor to operate causing nosepiece 50 to drive the nut (or otherfastening operation) until the torque being transmitted by the couplingassembly exceeds the pre-set value. As soon as the torque exceeds thispre-set value, relative movement takes place between input spindle 26and output spindle 44. As can best be seen in FIG, 3, as soon as inputspindle 26 rotates relative to output spindle 44, ball 84 is cammedinwardly, moving release member 76 pivotally about pin 78, allowing pushrod 72 to move to the right as seen in FIG. 2, down the notch 82. Thiscloses the valve member under the pressure differential of the inletfluid, and keeps the valve closed until the trigger 18 is released,venting chamber 20 and balancing the pressure across valve 52. At thispoint, the spring 86 returns valve 52 and push rod 72 to the cockedposition, and spring 80 returns release member 76 to the position shownin FIG. 2, thus resetting the shut-off assembly for the next operation.

While the forms of apparatus herein described constitute preferredembodiments, it is to be understood that the invention is not limited tothese precise forms of apparatus, and that changes may be made thereinwithout departing from the scope of the invention which is defined inthe appended claims.

What is claimed is:
 1. A power tool having a motor, an output shaft fortransmitting rotation to a tool bit; and a torque-limiting assemblycomprising adjustable torque transmitting means with a driving member, aco-axial driven member, a helical spring frictionally connecting saiddriving member and said driven member, the wire size of the springvarying from end-to-end, means for adjusting the position of said springaxially, and automatic shut-off means for interrupting the supply ofpower to said motor.
 2. A manually operable power tool having a motor,means for manual control of power to said motor, automatic shut-offmeans for interrupting the supply of power to said motor, atorque-limiting assembly for transmitting torque to the output shaft ofsaid tool, said torque-limiting assembly comprising a driving spindleconnected to the output of said motor, a driven spindle co-axial withand abutting said driving spindle, said driven spindle connected to saidoutput shaft, and a helical spring frictionally connecting said drivingmember and said driven member, said torque-limiting assembly havingmeans for operating said automatic shut-off means.
 3. The power tool ofclaim 2, in which said helical spring cross-sectional area uniformlyincreases in size from one end towards the other.
 4. The power tool ofclaim 3 in which means is provided for adjusting axially the position ofsaid helical spring connecting said driving member and said drivenmember.
 5. The power tool of claim 4 wherein said means for adjustingthe position of said helical spring comprises a threaded adjusting nut.6. A manually operable power tool comprising a motor, operator controlmeans for control of power to said motor, automatic shut-off means forinterrupting the supply of power to said motor, said shut-off meansremaining operable after initial automatic actuation until interruptionof power by said operator control means, after which said automaticshut-off means resets for the next cycle of operation, an adjustabletorque-limiting assembly for transmitting torque to the output shaft ofsaid tool, said torque-limiting assembly comprising a driving spindle,connected to the output of said motor, a driven spindle co-axial withand abutting said driving spindle, said driven spindle being connectedto said output shaft, a helical spring frictionally coupling saiddriving spindle and said driven spindle and being axially adjustablealong said driving and driven spindles, said helical springcross-sectional area increasing from the end over the output spindletowards the other end of said spring; and means connecting saidtorque-limiting assembly and said automatic shut-off means, whereby saidtorque-limiting assembly actuates said automatic shut-off means uponattaining the pre-set limit of torque.
 7. The power tool of claim 6wherein said helical spring is axially adjusted by a torque adjustingnut enclosing said helical spring.
 8. The power tool of claim 6 whereinsaid helical spring is wound so that increasing resistance to rotationtends to loosen said spring coils on said driven spindle.